High intensity light sources, and particularly white high intensity light sources, are interesting for various applications including spots and digital light projection. For such purposes, it is possible to make use of so-called light concentrators where shorter wavelength light is converted to longer wavelengths in a highly transparent luminescent material. Such a transparent luminescent material is illuminated by LEDs to produce longer wavelengths within the luminescent material. Converted light, which will be waveguided in the luminescent material, is extracted from a surface leading to an intensity gain.
Document WO 2012/056382 A1 describes in one embodiment a lighting device for such a purpose comprising more than one waveguide, of which one or more may be provided with a luminescent material arranged on or in the waveguide and configured to convert light from a light source into luminescent material emission.
However, in such a lighting device converted light which does not get coupled into the wave guide escapes from the side surfaces and this light gets lost resulting in a reduced efficiency.
Document WO 2006/054203 describes a light emitting device with a conversion structure which absorbs light from, in general blue, LEDs, converts it to light with longer wavelengths and guides it to an exit surface. In the conversion structure, nearly all blue light is converted into light of longer wavelengths. Any non-converted light, i.e. light remaining blue, is transmitted and not guided to the light exit surface, thereby resulting in loss of light and a reduced efficiency.
For a white light source, however, the presence of blue light as a part of the emission from the light exit surface is desired as well.
That is, both mentioned prior art documents describe devices in which an excessive amount of light loss occurs thereby compromising the intensity of the emitted light. Furthermore, for both prior art devices, the spectral distribution of the emitted light covers a too narrow wavelength region and is thus inadequate, particularly when used for white light sources.
WO2012/146960A1 describes an optical fiber which receives and guides a primary light in a longitudinal direction. Scattering structures in the optical fiber re-direct the primary light out of the optical fiber in the transverse direction into a photo-luminescent layer which converts the primary light to secondary light having a different wavelength than the primary light resulting in white light exiting the photo-luminescent layer.
US2008/0232084A1 describes a white light source device comprising a condenser lens which condenses light emitted from a blue LED source to enter an entrance face of a rod lens in which the light propagates and reducing the unevenness in brightness. At the exit surface of the rod lens a fluorescent material is arranged which results in white light.